The present invention relates to a video tape recorder and, more particularly to a tape timer apparatus used in the video tape recorder.
In a video tape recorder (VTR), a tape timer apparatus counts a tape time which indicates the amount the tape has run, and, therefore, the position of the tape being recorded or reproduced at this moment. In a prior art tape timer apparatus, such tape time is counted by an up/down counter assembly in response to a frame pulse which is used as a clock signal and a tape direction signal both delivered from the VTR. However, in a VTR applied for broadcasting use, the period indicated by a tape timer apparatus should range from a single frame period up to a ten hour period. In order to realize such a long period, the tape timer apparatus must use many up/down counters.
In a theoretical tape timer apparatus to be described herein, a microcomputer is used to count a tape time in response to the of receipt frame pulses and a tape direction signal. More specifically, the frame pulses are applied as an interruption demand signal to the microcomputer so that the microcomputer performs an addition or subtraction operation in accordance with the tape direction signal every time a frame pulse is received. This interruption step is conducted on the basis of the minimum period (frame period), and as the tape speed is increased during a fast forward or rewinding operation, the interval between interruption demand signals is shortened correspondingly. For instance, when the tape running speed is increased 50 times as high as normal speed, the interruption demand signal is generated at a time interval of 660 .mu.s. If the microcomputer does not have sufficient capacity to cope with such a high speed interruption demand signal, it is impossible to process all of interruption demands, resulting in an error in the counted data. In addition, a microcomputer employed in a current VTR is also used for performing operation control thereof other than counting the tape time. Therefore, when the tape speed becomes high, the operation control other than the tape time counting is not performed due to the high frequency interruption demands. To prevent this problem, it is necessary to use a microcomputer having a high processing speed exclusively for counting the tape time.
The above described problem would be overcome if the counting is made not in response to each frame pulse but in response to every fourth frame pulse. This countermeasure, however, makes it difficult to conduct a detailed edition on the frame unit in the tape edition.